Wireless communication systems are widely deployed to provide various kinds of communication services such as voice and data services. Generally, these communication systems are multiple access systems capable of supporting communication with multiple users by sharing available system resources (e.g., bandwidth and transmit power). Examples of multiple access systems include a Code Division Multiple Access (CDMA) system, a Frequency Division Multiple Access (FDMA) system, a Time Division Multiple Access (TDMA) system, an Orthogonal Frequency Division Multiple Access (OFDMA) system, and a Single Carrier Frequency Division Multiple Access (SC-FDMA) system.
Standards for Wireless Local Area Network (LAN) technology are being developed by the Institute of Electrical and Electronics Engineers (IEEE) 802.11 group. IEEE 802.11a and 802.11b use an unlicensed band at 2.4 or 5 GHz. IEEE 802.11b provides a transfer rate of 11 Mbps, while IEEE 802.11a provides a transfer rate of 54 Mbps. IEEE 802.11g applies Orthogonal Frequency Division Multiplexing (OFDM) at 2.4 GHz to provide a transfer rate of 54 Mbps. IEEE 802.11n applies Multiple Input Multiple Output-OFDM (MIMO-OFDM) to provide a data rate of 300 Mbps. IEEE 802.11n supports channel bandwidths up to 40 MHz. In this case, IEEE 802.11n provides a transfer rate of 600 Mbps. IEEE 802.11p is a standard for supporting Wireless Access in Vehicular Environments (WAVE). For example, IEEE 802.11p provides improvements needed to support Intelligent Transportation Systems (ITS). IEEE 802.11ai is a standard for supporting fast initial link setup for IEEE 802.11 stations (STAs).
A protocol related to Direct Link Setup (DLS) in a WLAN environment conforming to IEEE 802.11e presupposes a Basic Service Set (BSS) supporting Quality of Service (QoS), namely a Quality BSS (QBSS). In the QBSS, not only a non-access point (AP) STA but also an AP serves as Quality APs (QAPs) supporting QoS. In currently commercialized WLAN environments (e.g., WLAN environments conforming to IEEE 802.11a/b/g), most APs are legacy APs that do not support QoS even if non-AP STAs are Quality STAs (QSTAs) supporting QoS. As a result, currently commercialized WLAN environments are limited in that the DLS service is not available even to QSTAs.
With recent widespread application of short-range wireless communication technology such as Wi-Fi, devices are not only connected to each other over a local network but also directly connected to each other. One device-to-device direction connection technology based on Wi-Fi is Wi-Fi Direct.
Wi-Fi Direct is a network connectivity standard describing operation of a link layer. Since a rule or standard for applications is not defined on a higher layer, incompatibility and inconsistent operation occur in executing an application after connection between Wi-Fi Direct devices is established. To address this problem, a standard specification called Wi-Fi Direct Services (WFDS) that contains upper-layer applications is under development by the Wi-Fi Alliance (WFA).
WFA has announced a new standard for delivering data through direction connection between mobile devices, namely Wi-Fi Direct. Thereby, relevant industries are briskly developing technologies to satisfy the Wi-Fi Direct standard. In a strict sense, Wi-Fi Direct is a marketing term corresponding to a brand name. Technical standards for Wi-Fi Direct are collectively called Wi-Fi Peer-to-Peer (P2P). Accordingly, Wi-Fi Direct and Wi-Fi P2P may be used interchangeably in the present invention in discussing the Wi-Fi-based P2P technology. For a legacy Wi-Fi network, a typical Wi-Fi-embedded device accesses an Internet network by performing access via an AP. A method for data communication through direct device-to-device connection has been conventionally used by some users by being embedded in devices such as cell phones and notebook PCs equipped with wireless communication technology such as Bluetooth. However, this method provides low transfer rate and transmission coverage for actual use thereof is limited to 10 m. In particular, the method has a technical limit on perceived performance in an environment in which a large volume of data is transmitted or many Bluetooth devices are present.
Meanwhile, Wi-Fi P2P has added sections for supporting direct communication between devices while retaining most functions of the legacy Wi-Fi standard. Thereby, Wi-Fi P2P provides P2P communication between devices by sufficiently utilizing hardware and physical properties of Wi-Fi chip-embedded devices and simply upgrading software alone in most cases.
As is well known, Wi-Fi chips have increasingly been applied to devices from various fields including notebook PCs, smartphones, smart TVs, game consoles and cameras, and a sufficient number of suppliers and technology manpower have been created. However, software development for supporting the Wi-Fi P2P standard has not been activated yet. This is because relevant software that will allow convenient utilization of the Wi-Fi P2P standard has not been distributed since the standard was announced.
A P2P group includes a device acting as an AP on the existing infrastructure network. This device is referred to as the P2P Group Owner (GO) in the P2P standard. There may be various P2P Clients around the P2P GO. In a P2P group, only one device can serve as the P2P GO and the other devices act as client devices.
FIG. 1 shows typical P2P network topology.
As shown in FIG. 1, the P2P GO may be directly connected to a client having a P2P function or may be connected to a legacy client having no P2P function.
FIG. 2 illustrates a situation in which one P2P device forms a P2P group and at the same time acts as an STA of WLAN to connect to an AP.
As shown in FIG. 2, the P2P technology standard defines the illustrated operation mode of P2P devices as concurrent operation.
In order for a series of P2P devices to form a group, which of the devices is to be the P2P GO is determined by the values of Group Owner Intent of P2P Attribute ID. The values are set between 0 and 15. The P2P devices exchange these values and a device having the greatest value becomes the P2P GO. A legacy device that does not support Wi-Fi P2P technology may also belong to the P2P group. In this case, the role of the legacy device is limited to the function of access to an infrastructure network via the P2P GO.
According to the Wi-Fi P2P standard, the P2P GO transmits a beacon signal using Orthogonal Frequency Division Multiplexing (OFDM), and therefore the 11b standard is not supported, while 11a/g/n standard devices may be used as Wi-Fi P2P devices.
To ensure the operation of establishing connection between the P2P GO and P2P clients, the P2P standard includes the following four functions.
First, P2P Discovery deals with technical items such as device discovery, service discovery, group formation and P2P invitation. In device discovery, two P2P devices exchange device-related information such as device names or device types thereof with each other over the same channel. In service discovery, the devices exchange information related to a service for the devices to use through P2P. Group formation functions to determine which device is to be the P2P GO and to create a new group. P2P invitation functions to call a permanently formed P2P group or to cause a P2P device to participate in an existing P2P group.
Secondly, P2P Group Operation describes formation and completion of a P2P group, confection to the P2P group, communications in the P2P group, a service for P2P client discovery, operation of a persistent P2P group, and the like.
Thirdly, P2P Power Management describes a method for P2P device power management and a method for signal processing at the time a power saving mode begins.
Lastly, Managed P2P Device describes a method for one P2P device to form a P2P group and access an infrastructure network via a WLAN AP at the same time.
Hereinafter, properties of the P2P group will be described. The P2P group is similar to the legacy infrastructure Basic Service Set (BSS) in that the P2P GO serves as an AP and P2P clients serve as STAs. Accordingly, a P2P device needs to be equipped with software serving as the GO and client. P2P devices are distinguished from each other by using P2P device addresses such as MAC addresses. P2P devices perform communication in the P2P group using P2P interface addresses. In this case, the P2P devices need not use a globally unique ID address. The P2P group has a globally unique ID P2P group ID, which is configured by a combination of a Service Set Identifier (SSID) and a P2P device address of the P2P GO. The Wi-Fi P2P standard uses WPA2-PSK/AES for security. The life cycle of the P2P group includes a temporary connection mechanism and a persistent connection mechanism in which the same connection is attempted after a certain period of time. Persistent group corresponds to a method to enable quick reconnection of a P2P group by applying the same connection type with roles, certification, SSIDs, and P2P group ID of the devices cashed when the P2P group was formed.
Hereinafter, a method for Wi-Fi P2P connection will be described. Wi-Fi devices proceed through a two-phase connection procedure. The first phase is discovery in which two P2P devices discover (find) each other. The second phase is group formation in which the role of P2P GO or P2P client is determined between the discovered devices. The discovery phase allows P2P devices to be connected to each other. Specifically, the discovery phase consists of a search state and a listen state. In the search state, the devices perform active scanning using a Probe Request frame. To perform fast scanning, the scanning range is defined. Scanning is performed using social channels, namely channels 1, 6 and 11. A P2P device selects one of the three social channels and remains in the listen state. If the P2P device receives a Probe Request frame transmitted from another P2P device which is in the search state, it responds with a Probe Response frame. The P2P devices may continuously alternate between the search state and the listen state and reach a common channel. After the P2P devices discover each other, they use the Probe Request frame and the Probe Response frame to discover a device type, a manufacturer, or a familiar device name in order to be optionally associated with each other. In addition, to check an inter-device compatible service present in the P2P devices, service discovery may be employed. This is intended to determine whether a service provided in one device is compatible with another device. In the P2P standard, a specific service discovery standard is not defined. A P2P device user may search for proximate P2P devices and services provided by the devices and then quickly connect to a desired device or service.
Hereinafter, group formation, which is the second phase, will be described. When the P2P devices complete the discovery (find) phase described above, checking presence of the counterpart device is completed. The two P2P devices need to enter the GO negotiation phase for configuring a BSS based on the discovery phase. The negotiation phase is broadly divided into two sub-phases. One sub-phase is a GO negotiation phase, and the other sub-phase is a Wi-Fi Protected Setup (WPS) phase. In the GO negotiation phase, the devices negotiate for the role of P2P GO or P2P client and set an operating channel to be used in the P2P group. In the WPS phase, operation that is usually performed in the conventional WPS is performed. The operation includes exchange of PIN information input by a user of the device through, for example, a keypad and simple setup through a push button. In the P2P group, P2P GO plays a key role. P2P GO assigns a P2P interface address, selects an operation channel for the group, and sends a beacon signal containing various operation parameters. In the P2P group, only P2P GO is capable of transmitting the beacon signal. Using the beacon signal, the P2P devices quickly recognize P2P GO and participate in the group in the scan phase, which is an initial phase of connection. Alternatively, the P2P GO may initiate a P2P group session on its own. The P2P GO may initiate the P2P group session after using the method described above in the P2P discovery phase. The value for P2P GO playing such an important role is not a fixed value for a certain device, but is adjustable by an application or higher-layer service. Therefore, the developer may select a proper value for P2P GO according to the purpose of an application.
Next, P2P addressing will be described. A P2P device assigns a P2P interface address to be used, using a MAC address in the P2P group session. Herein, the P2P interface address of P2P GO is a BSS Identifier (BSSID), which is substantially the MAC address of P2P GO.
Hereinafter, disassociation of the P2P group will be described. If the P2P session ends, the P2P GO needs to inform all P2P clients of end of the P2P group session through deauthentication. The P2P clients may also perform disassociation for P2P GO. In this case, the clients need to go through a disassociation procedure, if possible. Upon receiving a disassociation request from a P2P client, the P2P GO may recognize that the P2P client has been disassociated. If the P2P GO senses an abnormal protocol error from a P2P client or a P2P client disturbing connection of the P2P group, it triggers rejection of authentication or denial of association. In this case, the P2P GO records a specific reason of failure in an association response and then transmits the response.